In general, a high frequency heating apparatus such as a microwave oven is provided with a switch attachment mechanism having a plurality of safety switches for stopping to generate a high frequency wave when a door of a heating chamber is opened. An attachment structure and an operational mechanism of the switch become complicated to provide a shielding protecting it from foreign subjects, e.g., dust and the like, and a safety mechanism securing a reliable operation of the apparatus by preventing a malfunction caused by a user's mistake.
Referring to FIG. 11, there is shown a first prior art switch attachment mechanism disclosed in Japanese Patent Laid-Open Publication No. 2000-156283. As shown, the first prior art switch attachment mechanism includes three switches 23, 24, 25; upper and lower hooks 27A, 27B; and three switch operating members 26A, 26B, 26C. Switches 23, 24, 25 are operated by respective corresponding switch operating members 26A, 26B, 26C rotated by hooks 27A, 27B. The structure of the first prior art switch attachment mechanism is rather complex and it takes time and skill to assemble components used therein since each component should be produced very accurately in dimension.
Referring to FIG. 12, there is shown a second prior art switch attachment mechanism disclosed in Japanese Patent Laid-Open Publication No. 2001-319769. In such a switch attachment mechanism, since two switches 23 and 24 are directly operated by upper and lower hooks 27A and 27B of door key 27 formed as a single body, it needs only one switch operating member 26 to operate switch 25. Accordingly, its structure is simpler than that of the first one. However, to ensure a reliable operation of the switch, switch operating member 26 of the second prior art switch attachment mechanism becomes complicated in structure and should be produced very accurately in dimension as well.
In order to overcome the above-mentioned problems, some of high frequency heating apparatus has recently employed a third switch attachment mechanism as shown in FIG. 13. In such a third switch attachment mechanism, since all of switches 23, 24, 25 are directly operated by hooks 27A and 27B of door key 27 as shown in FIG. 12, its structure can be further simplified.
In case of the prior art switch attachment mechanisms where the switches are operated by the hooks of the door key through at least one switch operating member, these switch attachment mechanisms become structurally complicated and it will take time and skill to assemble them since it should be manufactured very precisely in dimension.
In case of the prior art switch attachment mechanism where the switches are directly operated by the hooks of the door key, space around an actuator of the switch is exposed through a hole accommodating the lower hook. Accordingly, if a child's finger or foreign substances are inserted through the hole, it may cause a malfunction or a failure of the switch.